The present invention relates generally to apparatus for opening and closing a flexible screen of a greenhouse or the like and, more particularly, to apparatus for opening and closing a flexible screen which when closed maintains a controlled atmosphere in the greenhouse and when opened ventilates the same. The flexible sheet may comprise a plastic sheet which covers the outer surface of the greenhouse or a sheet material which partitions the interior of the greenhouse. The present invention relates to such apparatus wherein the winding rod winds the screen to open the same and unwind the screen to close the same.
Conventional apparatus of the type described above for opening and closing a flexible screen of a greenhouse are disclosed in Japanese published applications Nos. 24852/77 and 43638/77. Referring to FIGS. 1a and 1b which illustrate the conventional apparatus, a prime mover M is disposed on one end of a gable side in the trough portion defined between adjacent ceilings of a greenhouse of the multiple-ridge type. One end of a flexible driving shaft F is connected to the drive shaft S of the prime mover M while the other end of the flexible driving shaft F is connected to a pipe P for winding the screen A. The screen A is wound and unwound through the normal and reverse rotations of the prime mover M.
The conventional apparatus illustrated in FIGS. 1a and 1b are not entirely satisfactory. More particularly,it is effectively impossible to wind and unwind the screen A in the region having the width designated 1 shown in the drawings, i.e., in the region where the prime mover M and the flexible driving shaft F are disposed. Furthermore, in this conventional apparatus, since a reduction gear mechanism R is disposed between the prime mover M and the flexible driving shaft F and the load imposed on the pipe P is directly received by the flexible shaft F, when the winding width of the screen is large, it becomes necessary to provide a flexible driving shaft having an especially high strength, thereby resulting in the reduction of the flexibility of the flexible driving shaft thereby undesirably expanding the width 1.